Method for strengthening anaerobic digestion of organic solid waste through cooperation of micro-aerobic pretreatment and oxide of nano-iron

Abstract

The invention provides a method for strengthening anaerobic digestion of organic solid waste through cooperation of micro-aerobic pretreatment and oxide of nano-iron, and belongs to the technical field of environmental engineering. According to the method, the organic solid waste is subjected to micro-aerobic pretreatment according to the type of the organic solid waste so as to improve the concentration of soluble organic matters in the organic solid waste, then in the anaerobic digestion process, the adding concentration of oxide of nano-iron is determined according to the total COD in the organic solid waste, and the content of the organic solid waste is increased by adding the oxide of nano-iron. And the biogas yield (namely the volume biogas yield of the organic solid waste, namely the biogas yield of the organic solid waste per unit volume) is synergistically improved. According to the method, the organic matter degradation rate and the biogas production rate of anaerobic digestion of the organic solid waste are effectively increased, reduction and recycling treatment of the organic solid waste are achieved, generation of foul gas such as hydrogen sulfide in the anaerobic digestion process is greatly reduced, the biogas purification cost is reduced, the economic benefit of anaerobic digestion engineering is remarkably increased, and the method is suitable for popularization.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental engineering, and relates to a method for strengthening anaerobic digestion of organic solid waste by using micro-aerobic pretreatment in coordination with nano-iron oxide. Background Art

[0002] The disposal of organic solid waste has become an important development direction in the field of ecological and environmental protection. Anaerobic digestion uses fermentation bacteria and methanogens to degrade organic matter to produce methane, carbon dioxide and water under medium temperature (35°C) or high temperature (55°C) conditions, achieving organic solid waste reduction, stabilization, harmlessness and resource utilization. Anaerobic digestion can not only degrade organic matter, achieve reduction and stabilization, but also produce biogas as clean energy. It has become the best technical route for the disposal of organic solid waste such as sludge, kitchen waste, and crop straw.

[0003] Anaerobic digestion usually includes four stages: hydrolysis, acidification, acetic acid production, and methanogenesis. In actual operation, due to the presence of difficult-to-degrade organic matter in organic solid waste (for example, extracellular polymers in residual sludge, cellulose in crop straw, etc.), low activity of methanogens, and accumulation of intermediate products (volatile fatty acids VFA), anaerobic digestion projects have low gas production rates, poor benefits, and are difficult to operate efficiently and stably. At present, in order to solve the above-mentioned problems in anaerobic digestion of organic solid waste, the main method is to enhance pretreatment and add functional materials to improve the methane production efficiency and system operation stability. The pretreatment process of organic solid waste mainly includes heat treatment, ultrasonic treatment, microwave treatment, mechanical treatment, ozone treatment, alkali treatment, etc. Due to the problems of high energy consumption and high cost, it is difficult to apply and promote in actual projects. Functional materials that can be added to anaerobic digestion of organic solid waste include trace metal elements, conductive materials, etc. Among them, trace elements such as iron ions, cobalt ions, and nickel ions can increase the relative abundance of key microbial flora in anaerobic digestion (such as increasing the relative abundance of Methanosarcina in Archaea) and the activity of key biological enzymes (such as iron redox protease and pyruvate formate lyase), thereby improving the efficiency of anaerobic digestion; conductive nanomaterials such as ferroferric oxide and biochar can improve the efficiency of methanogenesis by promoting direct interspecies electron transfer (DIET) of anaerobic digestion microorganisms. However, since the cost of functional materials is usually high, the components of organic solid waste are complex, and the properties of each component are time-varying during continuous production and operation, it is difficult to determine the appropriate concentration of functional materials in actual anaerobic digestion projects. If the concentration is too low, the gas production efficiency will not be significantly improved. If the concentration is too high, the microbial activity will be inhibited, resulting in a decrease in the degradation rate of organic matter and the gas production rate.

[0004] Organic solid waste is the end product of human production and life, and is also a usable resource. Anaerobic digestion and biogas utilization can achieve organic solid waste reduction, stabilization, harmlessness and resource utilization. Under the severe situation of global water pollution and energy crisis, improving the efficiency and economic benefits of anaerobic digestion of organic solid waste is of great significance for building a resource-saving, environmentally friendly society and achieving sustainable development. Summary of the invention

[0005] The present invention provides a method for strengthening anaerobic digestion of organic solid waste by using micro-aerobic pretreatment in coordination with nano-iron oxide. The method effectively improves the organic matter degradation rate and biogas production rate (referring to the volumetric gas production rate of organic solid waste, i.e., the biogas production per unit volume of organic solid waste) of anaerobic digestion of organic solid waste, realizes the reduction and resource disposal of organic solid waste, and greatly reduces the generation of malodorous gases such as hydrogen sulfide during anaerobic digestion, reduces the cost of biogas purification, and significantly improves the economic benefits of anaerobic digestion projects.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a method for strengthening anaerobic digestion of organic solid waste by micro-aerobic pretreatment and synergistically using nano-iron oxides. Micro-aerobic pretreatment is performed on the organic solid waste according to its type to increase the concentration of soluble organic matter in the organic solid waste. Then, during the anaerobic digestion process, the addition concentration of nano-iron oxides is determined according to the total COD in the organic solid waste. The addition of nano-iron oxides synergistically improves the biogas production rate.

[0007] It is understandable that in this method, the organic solid waste is first pretreated with a microaerobic process, and the microaerobic pretreatment process parameters are determined according to the type of organic solid waste. By providing a microaerobic environment, the types of hydrolysis and acidification functional microorganisms in the anaerobic digestion system are enriched, the abundance and activity of key microbial populations are increased, and the macromolecular organic matter that is difficult to degrade in the organic solid waste is quickly hydrolyzed to produce small molecular organic matter that is easily utilized by anaerobic microorganisms, thereby increasing the concentration of soluble organic matter and providing sufficient substrate for the subsequent methane production stage. It is understandable that the organic matter (total COD) in the organic solid waste is divided into soluble organic matter and macromolecular insoluble organic matter. In order to further improve the gas production rate of anaerobic digestion, the macromolecular insoluble organic matter is degraded into small molecular soluble organic matter by strengthening pretreatment and adding functional materials, so as to improve the organic matter removal rate and methane production rate. During the anaerobic digestion process, the appropriate concentration of nano-iron oxide is determined based on the total COD in the organic solid waste. The activity of key methanogenic microorganisms and enzymes in the anaerobic digestion process is increased by adding nano-iron oxide. At the same time, nano-iron oxide, as an electron conductor, can promote direct interspecies electron transfer to improve methanogenesis efficiency, thereby increasing biogas production, increasing organic matter removal rate, and reducing the production of odorous gases such as hydrogen sulfide.

[0008] Preferably, the nano iron oxide is selected from any one of ferroferric oxide and nano iron oxide, wherein the particle size of nano ferroferric oxide is in the range of 20nm-10μm, preferably 80-100nm; the particle size of nano iron oxide is in the range of 20nm-10μm, preferably 100-200nm.

[0009] Preferably, when the addition concentration of nano-iron oxide is determined according to the total COD in the organic solid waste, when the added nano-iron oxide is nano-ferroferric oxide, the nano-ferroferric oxide is dispersed with a 1 mmol / L sodium dodecyl sulfate solution to form a 20000 mg / L nano-ferroferric oxide suspension, and the suspension is added;

[0010] When the added nano iron oxide is nano iron oxide, the nano iron oxide is dispersed with 1 mmol / L sodium dodecyl sulfate solution to form a 50000 mg / L nano iron oxide suspension, which is then added.

[0011] As a preferred method, during the anaerobic digestion process, the volume of nano-ferroferric oxide suspension added is V a =(0.001×b×V0) / (20000-0.001×b)~(0.007×b×V0) / (20000-0.007×b); where b is the total COD of organic solid waste, in mg / L; V0 is the volume of organic solid waste in the anaerobic digestion system, in L; V a , unit: L.

[0012] It can be understood that the added volume V of the nano-ferroferric oxide suspension is a It is calculated in the following way:

[0013] The total COD of the organic solid waste is detected as b (unit: mg / L), and the concentration of nano-ferroferric oxide added during anaerobic digestion should be controlled at 0.001×b~0.007×b, preferably 0.003×b (unit: mg / L); the volume of organic solid waste during anaerobic digestion is set as V0, and the volume of nano-ferroferric oxide suspension added is V a , we can get w=(V a ×20000) / (V a +V0), then the added volume V of nano-ferroferric oxide suspension can be calculated a The calculation method of V is as described above. a It is (0.003×b×V0) / (20000-0.003×b), unit is L.

[0014] As a preferred method, during the anaerobic digestion process, the volume of nano-iron oxide suspension added is V a(0.002×b×V0) / (50000-0.002×b)~(0.008×b×V0) / (50000-0.008×b);

[0015] Where b is the total COD of organic solid waste, in mg / L; V0 is the volume of organic solid waste in the anaerobic digestion system, in L; V a , unit: L.

[0016] It can be understood that the added volume V of the nano-iron oxide suspension is a It is calculated in the following way:

[0017] The total COD of the organic solid waste is detected as b (unit: mg / L), and the concentration of nano-iron oxide added during anaerobic digestion should be controlled at 0.002×b~0.008×b, preferably 0.0035×b (unit: mg / L); the volume of organic solid waste during anaerobic digestion is set as V0, and the volume of nano-iron oxide suspension added is V a , we can get w=(V a ×50000) / (V a +V0), then the added volume V of nano-iron oxide suspension can be calculated a The calculation method of V is as described above. a It is (0.0035×b×V0) / (50000-0.0035×b), unit is L.

[0018] Preferably, the types of organic solid waste include at least one of residual sludge from municipal sewage treatment plants, crop straw and garden waste, and restaurant kitchen waste.

[0019] Preferably, the organic solid waste is subjected to micro-aerobic pretreatment according to its type, specifically:

[0020] For the excess sludge from municipal wastewater treatment plants, the microaerobic process aeration ratio was set to 5 × 10 -6 ×b~1×10 -5 ×b vvm, pretreatment time is 12-24h, mechanical stirring rate is 50-80r / min; the preferred ventilation ratio is 8×10 -6 ×bvvm, pretreatment time was 15h, and mechanical stirring rate was 60r / min.

[0021] For crop straw and garden waste, the microaerobic process aeration ratio was set to 1 × 10 -5 ×b~2×10 -5 ×bvvm, pretreatment time is 16-28h, mechanical stirring rate is 50-90r / min; the preferred ventilation ratio is 1.5×10 -5×bvvm, pretreatment time was 22 h, mechanical stirring rate was 70 r / min;

[0022] For food waste, the microaerobic process aeration ratio was set to 3 × 10 -6 ×b~7×10 -6 ×b vvm, pretreatment time is 8-15h, mechanical stirring rate is 50-80r / min; the preferred ventilation ratio is 5×10 -6 ×b vvm, pretreatment time was 10 h, and mechanical stirring rate was 60 r / min.

[0023] Preferably, the organic solid waste is subjected to micro-aerobic pretreatment according to its type, specifically:

[0024] The volume proportions of residual sludge, crop straw, garden waste and kitchen waste in organic solid waste are n1, n2 and n3 respectively, n1+n2+n3=100%, COD is b1, b2 and b3 respectively, then the ventilation ratio is (5×10 -6 ×b1×n1+1×10 -5 ×b2×n2+3×10 -6 ×b3×n3)~(1×10 -5 ×b1×n1+2×10 -5 ×b2×n2+7×10 -6 ×b3×n3)vvm, the pretreatment time is 10 to 24 hours, the mechanical stirring rate is 50 to 90 r / min; n1, n2, and n3 are any values ​​within the range of 0% to 100%;

[0025] Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

[0026] As a preferred method, the ventilation ratio is (8×10 -6 ×b1×n1+1.5×10 -5 ×b2×n2+5×10 -6 ×b3×n3), the pretreatment time is (15×n1+22×n2+10×n3)h, and the mechanical stirring rate is (60×n1+70×n2+60×n3)r / min;

[0027] Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

[0028] Preferably, after the pretreatment, nitrogen is passed through the organic solid waste to remove oxygen, the nitrogen ventilation ratio is 0.2-0.8vvm, and the ventilation time is 2-5min; preferably, the nitrogen ventilation ratio is 0.5vvm, and the ventilation time is 3min.

[0029] As a preferred method, compared with only microaerobic pretreatment and only adding nano iron oxide, the biogas production rate is increased by 30-50% and 20-40% respectively.

[0030] Compared with the prior art, the advantages and positive effects of the present invention are:

[0031] The present invention provides a method for strengthening anaerobic digestion of organic solid waste by micro-aerobic pretreatment in coordination with nano-iron oxide, which effectively improves the organic matter degradation rate and biogas production rate of anaerobic digestion of organic solid waste. Compared with only micro-aerobic pretreatment and only adding nano-iron oxide, the biogas production rate is increased by 30-50% and 20-40% respectively, achieving the reduction and resource disposal of organic solid waste, and greatly reducing the generation of malodorous gases such as hydrogen sulfide during anaerobic digestion, reducing the cost of biogas purification, and significantly improving the economic benefits of anaerobic digestion projects. The method is suitable for popularization and application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A municipal sewage treatment plant in a northern coastal city has a treatment capacity of 100,000 cubic meters per day. 2 O (anaerobic-anoxic-aerobic) process, the total COD of the residual sludge was 38620 mg / L, and the pH was 6.75. 2L of residual sludge was taken respectively, and the inoculated sludge was the sludge from the anaerobic digester of the sewage treatment plant, and the volume ratio of the inoculated sludge to the residual sludge was 1:3; a blank control group, a microaerobic pretreatment control group, a control group with only nano-ferric oxide, and an experimental group were set up, and 3 parallel samples were set up in each group.

[0035] Blank control group: no pretreatment, no addition of nano-ferroferric oxide, the temperature of the sludge anaerobic digestion system was controlled at 35℃, and anaerobic digestion was carried out for 20 days.

[0036] Only microaerobic pretreatment control group: microaerobic pretreatment (ventilation ratio of 8×10 -6 ×b=8×10 -6 ×38620=0.3vvm, pretreatment time of 15h, stirring rate of 60r / min), no addition of nano iron oxide, ventilation ratio of 0.3vvm, pretreatment time of 15h, stirring rate of 60r / min, control the temperature of sludge anaerobic digestion system at 35°C, and carry out anaerobic digestion for 20d.

[0037] The control group in which only nano-iron oxide was added: no microaerobic pretreatment was performed, nano-ferroferric oxide with a particle size of 80 nm was selected, and a nano-ferroferric oxide suspension with a concentration of 20000 mg / L was prepared with 1 mmol / L sodium dodecyl sulfate solution; the preferred nano-ferroferric oxide suspension addition volume Va=(0.003×b×V0) / (20000-0.003×b)=(0.003×38620×2) / (20000-0.003×38620)=0.01165L=11.65mL, the temperature of the sludge anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0038] Experimental group: First, the sludge was subjected to microaerobic pretreatment (ventilation ratio was 8×10 -6 ×b=8×10 -6 ×38620=0.3vvm, pretreatment time is 15h, stirring rate is 60r / min). Then nitrogen is aerated through the sludge to remove oxygen, and the nitrogen aeration ratio is 0.5vvm; the aeration time is 3min. Select nano-ferroferric oxide with a particle size of 80nm, use 1mmol / L sodium dodecyl sulfate solution to prepare a nano-ferroferric oxide suspension with a concentration of 20000mg / L; the preferred nano-ferroferric oxide suspension addition volume Va=(0.003×b×V0) / (20000-0.003×b)=(0.003×38620×2) / (20000-0.003×38620)=0.01165L=11.65mL. Control the temperature of the sludge anaerobic digestion system at 35℃, and carry out anaerobic digestion for 20d.

[0039] The average cumulative biogas production and average hydrogen sulfide concentration in biogas for the above groups are summarized in Table 1.

[0040] Table 1

[0041]

[0042] As shown in Table 1, the average cumulative biogas production of the microaerobic pretreatment and nano-ferric oxide synergistic enhanced sludge anaerobic digestion group increased by about 44.3% and the hydrogen sulfide concentration decreased by 213 mg / m 3 Compared with the control group with only nano-ferric oxide, the average cumulative biogas production increased by about 39.4% and the hydrogen sulfide concentration decreased by 7 mg / m 3 Compared with the blank control group, the average cumulative biogas production increased by about 72.0%, and the hydrogen sulfide concentration decreased by about 225 mg / m 3Compared with conventional anaerobic digestion processes, micro-aerobic pretreatment and the addition of nano-ferric oxide can synergistically enhance sludge anaerobic digestion, which can greatly increase the biogas production rate, significantly reduce the production of malodorous gases such as hydrogen sulfide during anaerobic digestion, reduce biogas purification costs, and significantly improve the economic benefits of anaerobic digestion projects.

[0043] Example 2

[0044] A municipal sewage treatment plant in a northern coastal city has a treatment capacity of 100,000 cubic meters per day. 2 O (anaerobic-anoxic-aerobic) process, the total COD of the residual sludge is 38620 mg / L, and the pH is 6.75; the food waste comes from the slurry after screening and crushing of a food waste treatment plant in a coastal city in the north, with a moisture content of 88.5% and a total COD of 183250 mg / L. 1.5L of residual sludge and 0.5L of food waste slurry were taken as mixed organic solid waste (the volume of residual sludge accounted for 75% and the volume of food waste accounted for 25%), and the total COD of the mixed organic solid waste was 74778 mg / L. The inoculated sludge was the sludge from the anaerobic digester of the sewage treatment plant, and the volume ratio of the inoculated sludge and the mixed organic solid waste was 1:3; a blank control group, a microaerobic pretreatment control group, a control group with only nano-iron oxide added, and an experimental group were set up, and 3 parallel samples were set up in each group.

[0045] Blank control group: No pretreatment was performed, no nano-iron oxide was added, the temperature of the mixed organic solid waste anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0046] Only microaerobic pretreatment control group: microaerobic pretreatment (ventilation ratio of 5×10 -6 ×38620×75%+3×10 -6 ×183250×25%=0.28vvm, pretreatment time is 10h, stirring rate is 50r / min), no nano iron oxide is added, the temperature of the sludge anaerobic digestion system is controlled at 35°C, and anaerobic digestion is carried out for 20 days.

[0047] The control group in which only nano-iron oxide was added: no microaerobic pretreatment was performed, nano-iron oxide with a particle size of 100 nm was selected, and a nano-iron oxide suspension with a concentration of 50000 mg / L was prepared with 1 mmol / L sodium dodecyl sulfate solution; the preferred nano-iron oxide suspension addition volume Va=(0.0035×b×V0) / (50000-0.0035×b)=(0.0035×74778×2) / (50000-0.0035×74778)=0.01052L=10.52mL, the temperature of the mixed organic solid waste anaerobic digestion system was controlled at 35°C, and anaerobic digestion was carried out for 20 days.

[0048] Experimental group: First, the mixed organic solid waste was subjected to microaerobic pretreatment (ventilation ratio of 8×10 -6 ×b=8×10 -6 ×38620=0.3vvm, pretreatment time is 15h, stirring rate is 60r / min). Then nitrogen is passed through the mixed organic solid waste to remove oxygen, and the nitrogen ventilation ratio is 0.5vvm; the ventilation time is 3min. Select nano iron oxide with a particle size of 100nm, use 1mmol / L sodium dodecyl sulfate solution to prepare a nano iron oxide suspension with a concentration of 50000mg / L; the preferred nano iron oxide suspension addition volume Va=(0.0035×b×V0) / (50000-0.0035×b)=(0.0035×74778×2) / (50000-0.0035×74778)=0.01052L=10.52mL. Control the temperature of the mixed organic solid waste anaerobic digestion system at 35℃, and carry out anaerobic digestion for 20d.

[0049] The average cumulative biogas production and average hydrogen sulfide concentration in biogas for the above groups are summarized in Table 2.

[0050] Table 2

[0051]

[0052] As shown in Table 2, the average cumulative biogas production of the microaerobic pretreatment and nano-iron oxide synergistic enhanced sludge anaerobic digestion test group increased by about 26.6% and the hydrogen sulfide concentration decreased by 516 mg / m 3 Compared with the control group with only nano-iron oxide, the average cumulative biogas production increased by about 24.8% and the hydrogen sulfide concentration decreased by 4 mg / m 3 Compared with the blank control group, the average cumulative biogas production increased by about 56.2% and the hydrogen sulfide concentration decreased by about 524 mg / m 3 Compared with conventional anaerobic digestion processes, micro-aerobic pretreatment and the addition of nano-iron oxide can synergistically enhance sludge anaerobic digestion, which can greatly increase the biogas production rate, significantly reduce the production of malodorous gases such as hydrogen sulfide during anaerobic digestion, reduce biogas purification costs, and significantly improve the economic benefits of anaerobic digestion projects.

Claims

1. A method for strengthening anaerobic digestion of organic solid waste by microaerobic pretreatment and nano-iron oxide, characterized in that: According to the type of organic solid waste, micro-aerobic pretreatment is carried out on it to increase the concentration of dissolved organic matter in the organic solid waste. Then, during the anaerobic digestion process, the addition concentration of nano-iron oxide is determined according to the total COD in the organic solid waste. The addition of nano-iron oxide can synergistically improve the biogas production rate.

2. The method according to claim 1, characterized in that The nano iron oxide is selected from any one of ferroferric oxide and nano iron oxide, wherein the particle size of nano ferroferric oxide is in the range of 20nm-10μm, preferably 80-100nm; the particle size of nano iron oxide is in the range of 20nm-10μm, preferably 100-200nm.

3. The method according to claim 2, characterized in that When the addition concentration of nano iron oxide is determined according to the total COD in the organic solid waste, when the added nano iron oxide is nano ferroferric oxide, the nano ferroferric oxide is dispersed with 1 mmol / L sodium dodecyl sulfate solution to form a 20000 mg / L nano ferroferric oxide suspension, and the suspension is added; When the added nano iron oxide is nano iron oxide, the nano iron oxide is dispersed with 1 mmol / L sodium dodecyl sulfate solution to form a 50000 mg / L nano iron oxide suspension, which is then added.

4. The method according to claim 3, characterized in that During the anaerobic digestion process, the volume of nano-ferroferric oxide suspension added is V a (0.001×b×V0) / (20000-0.001×b)~(0.007×b×V0) / (20000-0.007×b); Nano-iron oxide suspension addition volume V a (0.002×b×V0) / (50000-0.002×b)~(0.008×b×V0) / (50000-0.008×b); Where b is the total COD of organic solid waste, in mg / L; V0 is the volume of organic solid waste in the anaerobic digestion system, in L; V a , unit: L.

5. The method according to claim 1, characterized in that: The types of organic solid waste include at least one of residual sludge from municipal sewage treatment plants, crop straw and garden waste, and food waste.

6. The method according to claim 5, characterized in that According to the type of organic solid waste, micro-aerobic pretreatment is carried out, specifically: For the excess sludge from municipal wastewater treatment plants, the microaerobic process aeration ratio was set to 5 × 10 -6 ×b~1×10 -5 ×bvvm, pretreatment time is 12-24h, mechanical stirring rate is 50-80r / min; For crop straw and garden waste, the microaerobic process aeration ratio was set to 1 × 10 -5 ×b~2×10 -5 ×b vvm, pretreatment time is 16-28h, mechanical stirring rate is 50-90r / min; For food waste, the microaerobic process aeration ratio was set to 3 × 10 -6 ×b~7×10 -6 ×b vvm, pretreatment time is 8 to 15 h, and mechanical stirring rate is 50 to 80 r / min.

7. The method according to claim 6, characterized in that According to the type of organic solid waste, micro-aerobic pretreatment is carried out, specifically: The volume proportions of residual sludge, crop straw, garden waste and kitchen waste in organic solid waste are n1, n2 and n3 respectively, n1+n2+n3=100%, COD is b1, b2 and b3 respectively, then the ventilation ratio is (5×10 -6 ×b1×n1+1×10 -5 ×b2×n2+3×10 -6 ×b3×n3)~(1×10 -5 ×b1×n1+2×10 -5 ×b2×n2+7×10 -6 ×b3×n3)vvm, the pretreatment time is 10 to 24 hours, the mechanical stirring rate is 50 to 90 r / min; n1, n2, and n3 are any values ​​within the range of 0% to 100%; Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

8. The method according to claim 7, characterized in that The ventilation ratio is (8×10 -6 ×b1×n1+1.5×10 -5 ×b2×n2+5×10 -6 ×b3×n3), the pretreatment time is (15×n1+22×n2+10×n3)h, and the mechanical stirring rate is (60×n1+70×n2+60×n3)r / min; Wherein, b is COD, unit is mg / L; ventilation ratio, unit is vvm, which is the ratio of ventilation volume per minute to the volume of pretreated organic solid waste.

9. The method according to claim 1, characterized in that: After the pretreatment, nitrogen is passed through the organic solid waste to remove oxygen. The nitrogen ventilation ratio is 0.2-0.8vvm and the ventilation time is 2-5min.

10. The method according to any one of claims 1 to 9, characterized in that: Compared with only microaerobic pretreatment and only adding nano iron oxide, the biogas production rate is increased by 30-50% and 20-40% respectively.

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